1. Field of the Invention
The present invention relates to a printing apparatus and a control method therefor and, particularly, to a printing apparatus including an inkjet printhead and an inkjet printhead control method used in the apparatus.
2. Description of the Related Art
Among printing apparatuses which are used as printing means for images, characters, and the like in a printer, copying machine, or facsimile apparatus, inkjet printing apparatuses (to be simply referred to as printing apparatuses hereinafter) perform printing by discharging ink from an inkjet printhead (to be simply referred to as a printhead hereinafter) onto a printing medium.
The printing apparatuses are roughly classified into a serial type printing apparatus which performs printing while scanning the printhead in a direction intersecting the conveyance direction of the printing medium, and a line type printing apparatus which performs printing while holding, at a fixed position, a full-line printhead having a print length corresponding to the full width of the printing medium. The above-described serial type printing apparatus generally sets a printing medium at a predetermined position, and repeats reciprocal movement of a carriage including the printhead in a predetermined direction on the printing medium and paper conveyance by a predetermined amount, thereby printing images on the entire surface of the printing medium.
A printing apparatus which supports color printing and has an arrangement including a plurality of printheads each corresponding to one ink color has become widespread.
A printing apparatus generally includes a recovery unit which removes thickened ink within a nozzle of a printhead and dust attached to the ink discharge surface of the printhead, and maintains stable ink discharge by operating this unit. An example of a recovery operation is an ink discharge operation (preliminary discharge operation) without printing on a printing medium, which enables to discharge thickened ink. The recovery unit includes, for example, a cap member which caps the ink discharge surface of the printhead while no printing is performed in order to prevent drying and evaporation of ink, and a suction pump which sucks thickened ink and the like from a nozzle of the printhead via the cap member.
If a suction recovery operation is performed by capping, by one cap, the ink discharge surface of a printhead including a plurality of nozzle arrays each corresponding to one ink color and formed by a plurality of nozzles, inks of the plurality of colors are mixed and refilled in the cap. If the cap member is separated from the ink discharge surface after the suction recovery operation in this state, mixed color ink remaining on the ink discharge surface of the printhead may enter a nozzle, and mix with the ink within the nozzle. Therefore, ink of a color different from an original ink color may be discharged from the printhead, thereby disabling, for example, printing with desired color on the printing medium.
To prevent this problem, for example, Japanese Patent Laid-Open No. 2002-137419 proposes an arrangement in which an air communication port capable of communicating with the outer air is provided in a cap, and the air communication port is communicated with the outer air after a suction operation to perform a preliminary discharge operation while performing the suction operation, thereby discharging mixed color ink.
On the other hand, if a preliminary discharge operation is performed with the printhead separated from the cap, satellites accompanying ink droplets, satellites created when some of ink droplets attached to the cap splash around, or the like float within the printing apparatus, thereby causing an ink mist. To suppress the occurrence of an ink mist, for example, Japanese Patent Laid-Open No. 2004-90233 proposes an arrangement in which if a preliminary discharge operation is performed the number of times equal to or larger than a predetermined value, the preliminary discharge operation is performed within a cap while it contacts the ink discharge surface of a printhead.
If, however, a preliminary discharge operation is performed within a cap while it contacts the ink discharge surface of a printhead as in the above-described conventional example, ink may collect in the cap and the ink liquid surface in the cap may reach near a nozzle. If the preliminary discharge operation continues after the ink liquid surface reaches near the nozzle, ink droplets discharged to the ink liquid surface may create bubbles on the liquid surface of the ink collecting in the cap, and the bubbles may enter the nozzle. This causes a discharge failure, thereby decreasing the quality of printing.
Furthermore, if the ink liquid surface reaches the distal end of the nozzle provided on the ink discharge surface, mixed color ink may enter the nozzle.